THE FAR-ULTRAVIOLET DUST ALBEDO IN THE UPPER-SCORPIUS SUBGROUP OF THE SCORPIUS-OB2 ASSOCIATION

During NRL's Far Ultraviolet Cameras experiment on STS-39, four images of the giant reflection nebula encompassing the Upper Scorpius subgroup of the Sco OB2 association were obtained in two ultraviolet bandpasses with lambda(eff) = 1362 Angstrom and 1769 Angstrom. From these images and IUE and TD-1 stellar spectra, the ratio of nebular to stellar flux was calculated. The ratio ranged from 0.577 to 0.921 at 1362 Angstrom and 0.681 to 0.916 at 1769 Angstrom with the spread in the ratio arising mainly from uncertainties in the sky background. In order to analyze these images, a model utilizing Monte Carlo techniques to describe radiative transfer in a spherical nebula with asymmetrically distributed stars was developed by elaborating on previous work by Witt (1977). This model was used to determine the range of albedos reproducing the observed nebular-to-stellar flux ratios while allowing the scattering phase function asymmetry to vary between 0.0 and 0.8. The resulting albedos were 0.47-0.70 at 1362 Angstrom and 0.55-0.72 at 1769 Angstrom.